This invention relates to asynchronous transfer mode (ATM) data networks. In particular, this invention relates to ATM data networks having so-called permanent virtual circuit (PVC) data paths that are automatically re-configured in an attempt to maximize network efficiency and capacity.
ATM-format data and ATM networks are well known in the data and communications art. Briefly, in an ATM network, data is routed from a source to a destination over a path that is comprised of one or more ATM switches. An ATM switch receives ATM data packets on an incoming port or terminal and routes the ATM data packets out on an outgoing port or terminal. The outgoing port of one ATM switch is frequently coupled to an input port of another ATM switch. Eventually, the data is routed through the switches of an ATM network to its destination where it is to be used.
Most ATM networks include numerous ATM switches, each receiving incoming data packets and routing data to some other switch in the network. As is well known in the art, the several switches of an ATM network receive data packets that are addressed to only the next ATM switch that comprise the path over which data is sent from a source to a destination.
Virtually all ATM switches are software controlled, allowing for increased functionality, among other things. At least one feature of a software-based ATM switch is the ability to set up and tear down connections through the actual switching fabric through which data passes between a switch input port and a switch output port. The ability to specify a path through the switch enables the ATM to route data along its way to a destination.
In an ATM network, at least one type of path is a so-called permanent virtual circuit or PVC which is a path through the network that is typically set up once. Setting up a PVC requires that each of the ATM switches through which data is to be routed, be programmed to connect incoming data on a particular transmission media onto a particular outgoing data port by which the data can be delivered to its destination. Unlike a so-called switched virtual circuit or SVC by which a data path through an ATM network can change during the course of a call, a PVC is a relatively long-life path through an ATM network.
Many ATM network operators monitor the traffic loading on the PVCs in their networks so as to adjust the data paths through the network to maximize network efficiency. In fact, many ATM switches are pre-programmed to continuously optimize data capacity through the network by re-routing a customer""s data from one PVC to another PVC. In some instances, the PVC over which a customer""s data is carried is torn down after the data stream is routed onto another PVC. Re-routing data almost always causes at least some data loss.
Optimizing network capacity frequently requires that a data stream (the data transferred between a source and destination or the data of a particular customer of the ATM network provider) is re-routed through the network for network reliability or to maintain network capacity or for other reasons. Notwithstanding the fact that ATM switches are computer controlled and the switching software and switching hardware operates at what many consider to be blinding speed, rerouting data through PVCs in an ATM network in pursuit of network optimization almost always causes some of the data of a data stream to be lost. This also impacts system real time by requiring the system to change routes.
Data loss caused by automatic path optimization requires that the lost data be re-transmitted. To a customer of the ATM network, lost data because of automatic path optimization can appear to be a network fault. Having to needlessly re-transmit data that is needlessly lost because of automatic optimization can frustrate the customers of the ATM network service provider.
A method for controlling automatic optimization of circuits through ATM switches and networks might reduce needless data loss and actually improve customer satisfaction by reducing the number of times that a data stream is interrupted and thereby reduce the data lost that almost always accompanies a circuit or network optimization.
In an ATM switching network made up of several ATM switches through which PVCs are established, many ATM switches are programmed to automatically re-configure or re-define a PVC periodically so as to maximize system capacity or to balance the data loading on the switches and their associated links. As most ATM switches are currently designed, re-configuring a PVC in an ATM network requires that a data stream routed over one or more data links and through one or more switches be changed to run through one or more different switches in order to route the data over different links. Even when a data path switch is performed automatically, changing a data path over which a data stream is carried almost always causes a data loss, requiring data retransmission. In many instances it might be preferable to refrain from automatically re-optimizing a PVC path.
Data loss due to automatic network optimization can be minimized while maintaining network optimization by tracking the history of optimizations done on a customer""s data stream and inhibiting subsequent automatic optimizations until some event has occurred. Briefly the method includes: a) tracking the history of path optimization for at least one particular data stream through a network, including identifying the PVC or data path through the network for that particular data stream at least some period of time; b) recording the occurrence of at least the most recent automatic PVC re-configuration for the data stream; c) inhibiting any subsequent (or second) automatic re-configurations of the PVC carrying the data stream through said ATM network until after the occurrence of some predetermined event, such as the passage of some length of time.